When a video program created in a foreign country is reproduced, subtitles are sometimes displayed at a lower portion or a right side of the screen. In video disc programs and conventional television broadcast programs, such subtitles have been superimposed in video pictures.
On the other hand, in the CAPTAIN (Character and Pattern Telephone Access Information Network System) serviced in Japan), such subtitles are sent as character code or dot patters. In the CD-G (Graphics) system, with subcode used to record graphics data, subtitles can be recorded.
Next, the data format of the CD-R system will be described. As shown in FIG. 17A, data of one frame is composed of subcode of one byte and data of 32 bytes.
The 32-byte data is composed of 24-byte audio data and eight-byte error correction code. The 24-byte audio data is composed of 12 samples. Six samples are assigned to each of L and R channels. Each sample is composed of two bytes.
In addition, as shown in FIG. 17B, one block is composed of subcode of 98 frames. FIG. 17C shows the content of one block. As shown in FIG. 17C, subcode of the individual frames is represented with eight channels P, Q, R, S, T, U, V, and W. The subcode of the first two of the 98 frames are sync patterns S0 and S1. In the subcode of the remaining 96 frames, various subcode data can be recorded.
However, track search data has been assigned to data of P and Q channels of subcode of one byte (individual bits are denoted by P to W). Thus, graphics data can be assigned to 6.times.96 bits of the remaining channels R to W.
Since data of one block is set at a frequency of 75 Hz, the data rate of one frame becomes 75.times.98 bytes. Thus, the data rate of subcode is 7.35 kbytes/sec.
FIG. 18 shows a transmission format of such graphics data. As shown in FIG. 18, one packet is composed of 96 symbols. One symbol is composed of data of six bits of each of channels R to W. In addition, one packet is composed of four packs. Each pack is composed of a total of 24 symbols that are symbols 0 to 23. Mode information is assigned to three bits R, S, and T of the symbol 0. Item information is assigned to three bits U, V, and W of the symbol 0. With a combination of the mode information and item information, modes shown in Table 1 are defined.
TABLE 1 ______________________________________ Mode Item ______________________________________ 000 000 0 mode 001 000 Graphics mode 001 001 TV graphics mode 111 000 User mode ______________________________________
An instruction has been assigned to the symbol 1. A mode, an item, and a parity against an instruction have been assigned to the symbols 2 and 3. Thus, an area for graphics data is substantially 12 symbols ranging from the symbol 4 to the symbol 19. A parity for 20 symbols ranging from the symbol 0 to the symbol 19 is assigned to four symbols ranging from the symbol 20 to the symbol 23.
In such a manner, in the CD-G system, graphics data can be assigned as binary data to an area of 6.times.12 pixels of each pack. The data rate of packs is 75 (Hz).times.4=300 packs/sec. Assuming that one character is assigned to the area of 6.times.12 pixels, 300 characters can be sent per second.
Since one screen defined in the CD-G system is composed of 288 horizontal pixels.times.192 lines, as given by the following expression, it takes 2.56 sec. to send characters for one screen. EQU [(288/6).times.(192/12)/300=2.56]
In this case, to represent data in hexadecimal notation, each pixel requires four bits. Thus, for one character pattern, four different patters should be sent. Consequently, the resultant transmission time amounts to 10.24 sec. that is four times 2.56 sec.
However, when an error takes place in video data, graphics data, or pixel data such as subtitle data that has been compressed and encoded by for example the run-length encoding method or DPCM encoding method, the remaining data of the current line is not correctly displayed. Thus, the use cannot comfortably see the resultant picture on the display.
To solve this problem, a structure for causing data of a frame/field that has an error not to be output may be used. Alternatively, a structure for causing such data to be muted may be used. However, from a point of view of the user, it is not convenient to cause data that has an error not to output at all. For example, it is desired to accomplish a function of which in the case that the degree of an error is low, data that has the error is interpolated with other data and in the case that the degree of the error is large, the data that has the error is not output.